Friday, 23 February 2018

Sometimes timing is funny. In November 2017 I wrote a post defending the Przewalski's horse's status as a wild animal. A new study by Orlando et al. has challenged the status of the Przewalski's horse as the last living genuine wild horse.The earliest archaeological evidence of horse husbandry is from the Botai culture of Kazakstan from 5.500 years ago. It has been assumed previously that these Botai horses belong to the earliest strain of domestic horses of the caballine lineage. Surprisingly, the authors found only about 2,7% Botai-related ancestry for all domestic horses from 4.000 years ago, while the authors claim the Botai horses turned out to be the ancestral stock of the modern Przewalski's horses population. I have not read the paper yet because it is behind a paywall, thus I cannot see what led the authors to the conclusion that all modern Przewalski's horses descend from the Botai population and not just that the Botai population was part of the przewalskii clade. But let us assume the former is the case for now.The authors thus write that Przewalski's horses are feral descendants of these early domestic horses, and not true wild horses. I have problems with the latter part of the conclusion. First of all, the horses of the Botai culture must have been in a very early state of domestication, and not for a long time. After escaping human husbandry, those early domestic horses have been exposed to natural selection for four millennia again. Any changes that might have occurred in the early state of domestication must have adapted to the requirements of living as a wild animal again. Thus, I don't regard the short (in evolutionary terms) episode of domestication as substantial enough to categorize the Przewalski's horse as feral instead of a wild animal. In fact, ever since its discovery, the Przewalski's horse has been used as a model for a wild equine and numerous differences in physiology, development and behaviour have been noted between the Przewalski's horse and domestic caballine horses as much as feral caballine horses. Przewalski's horses are way less tamable and more aggressive than domestic caballine horses, and genomic studies have shown that numerous genes for physiological aspects have been altered through human utilization while that is not the case in the Przewalki's horse[1]. The recent study by Orlando et al., or to be precise the short period of early domestication, does not alter this fact. The situation is not comparable to mustangs and other feral caballine populations at al.Thus I do not regard the Przewalski's horse as any less wild as before. One could use it as an example for a "post-domestic wildtype", a term I tried to introduce in my posts on dedomestication as opposed to "pre-domestic", a term that is already used. However, I am rather confident that the majority of authors will begin to list the Przewalski's horse as a feral horse now, as the 19th century conception of nature and evolution as something static and humans as an irreversible altering factor is still prevalent in a lot of experts heads. Unfortunately, in my opinion.Interestingly, the authors found the alleles for the Leopard spotted colour present in the Botai horses. This colour variant has already been found in Pleistocene wild horses (see earlier studies of Orlando et al.).LiteratureOrlando et al. 2018: Ancient genomes revisit the ancestry of domestic and Przewalski's horses.[1] Schubert et al.: Prehistoric genomes reveal the genetic foundation and costs of horse domestication. 2014.

Monday, 19 February 2018

In
Biological basics III: The species concept – a complicated issue, I gave a
little overview over how a species is usually defined and what a species
actually is. Today’s post is going to look at subspecies. The understanding of
the concept of a subspecies is necessary for some aspects of “breeding-back”,
such as the issue of using zebus in aurochs projects and, more essentially, the
Quagga project. Subspecies are sometimes called a cop-out, nit-picking or
something for bored taxonomists, and I am going to outline why this critique is
not fact-based.

Subspecies – something for bored taxonomists?

The short and
definite answer to this is No. As Charles Darwin already noticed absolutely
correctly and perfectly subsumed, subspecies are incipient species and the line between varieties, subspecies and
species is gradual. As he noted in his opus magnum, On the origin of species, species are basically “strongly marked
varieties”, and subspecies are a state in between. And as the previous post on
hybridization has shown, even the line between species is blurred because many
closely related species are able to hybridize with limited or unlimited
fertility. In many cases there is uncertainty on whether two or more species
should be regarded as subspecies of one species, or whether two or more
subspecies should be elevated to species level. However, for this section on
the concept of a subspecies and what justifies it from a biological point of
view, I will try to focus on examples for which there is a consensus.

Subspecies
are in a beginning state of cladogenesis, a speciation mode that I already
explained in part I. It is the case when populations diverge and become more or
less isolated, and the allelic frequencies start to change due to genetic
drift, mutation and selection. These changes not only concern neutral genetic
variations but all biological aspects: morphology, behaviour, ecology. This is
especially enforced by the fact that the different populations often experience
different selective pressure due to a different environment. This is particularly
true in species with a large geographical range, especially when it is disjunct
(isolation). Thus, the different populations become regionally adapted
additionally to coincidental differences caused by genetic drift. In some
cases, the differences between populations or group of populations assigned to
different subspecies may concern only single traits like colour variants, but
in some cases the differences are well-marked and concern a number of
biological aspects. I am going to go over some examples.

The
classification of subspecies experiences the typical taxonomical problems of
subjectivity and tradition, and therefore is not always consistent. In some
cases two subspecies might be as distinct as a pair of species, and vice versa.
There is no clear line as taxonomy is an artificial system that aims to
classify the complex reality of organismic relationships.

One example
clear example of a species that is divided into two subspecies is the American Bison
Bisonbison. This species is divided into a northern subspecies, the wood
bison B. b. athabascae, and a
southern one, the plains bison B. b.
bison. Both differ ecologically and morphologically; wood bison dwell boreal
forest regions and are adapted to lower temperatures, while plains bison live
in more open regions and are less (but still very) cold-adapted. Wood bison are
larger, have a darker pelage and less hair on the forelegs and beard. Also, the
hump is shaped differently.

The African
buffalo, Synceruscaffer, is divided into five subspecies.
The nominate form, Synceruscaffercaffer, has the southernmost range, is the largest subspecies and
very dark in colour. S. c. brachyceros, is smaller, weights only
half as much and is lighter in colour. The smallest subspecies, the forest
buffalo S. c. nanus, differs
considerably ecologically and morphologically. It inhabits the swampy forest
areas of Central and West Africa instead of dry grasslands, it is very small
(withers height less than 120cm), a bright orangish-red colour instead of
greyish to black-brown, small horns and brushy hair on the ears. Some authors
have suggesting listing it as a separate species, and since the Caucasian
wisent which differs from the nominate form less drastically is considered a
separate species now (Bison caucasicus),
I definitely list the forest buffalo as a separate species, Syncerus nanus. This is a good example
that shows that taxonomy is often subjective and not consistent.

A prime
example for a species with a large geographical range and many different
subspecies that are morphologically and ecologically distinct is the wolf, Canislupus. Its large, Holarctic distribution includes more than a dozen
subspecies that all differ in colour and morphology, body size, environmental
adaptions, and to a certain degree behaviour. For example, large subspecies
such as the nominate form C. l. lupus
weight twice as much as smaller subspecies such as the Arabian wolf C. l.
arabis or pale-footed wolf and have a stronger and more robust build;
smaller wolves live in smaller packs and are less macropredatory. Wolf
subspecies can be adapted to totally different climates; the Arabian wolf for
example inhabits the hot arid climate of the Arabian peninsular, while the
polar wolf C. l. artcos obviously is
adapted to arctic conditions. Wolf subspecies also differ in colour nuances.

Another
predatory species that has a large range that includes many different
subspecies with different morphological characteristics is the lion, Panthera leo. Lion subspecies can be
adapted to different ecologic environments and may differ in body size and mane
for example, and the diversity in the species becomes even greater if you
include Pleistocene forms.

There are
many other examples in all possible vertebrate groups that show that subspecies
are clear evolutionary lines with distinct morphological, ecological or
ethological traits. In some cases the situation is more clear and distinct as
in others, but subspecies are definitely not something for “bored taxonomists”.
It makes sense to differentiate subspecies not only from a taxonomical
standpoint, it also appreciates the evolutionary, ecological, morphological and
ethological situation within a species. Therefore, subspecies are a very useful
and justified concept, which is followed by all zoologists (quite frankly, I
have never heard of any zoologist deeming the subspecies concept as not useful
and not using it).

A special
case of evolutionary variation within a species is the so-called cline. In this
case there is not a clear differentiation into several lineages, but variation
along a geographic or ecologic gradient. This is comparable to the concept of a
ring species that has been explained in the previous post. The quagga, Equusquaggaquagga, has been
suggested by some to represent the end of a cline rather than a distinct
subspecies, although I think this should be backed up by empirical evidence
(see this post on the quagga).

Monday, 12 February 2018

Having had
a look at how species are usually defined, this post is on the result of the
reproduction between two distinct species – hybrids. More precisely, with this
post I want to illustrate the role of hybridization in evolution and to show
that hybrids are neither Frankenstein creations of bored farmers or zoos, or
signs of the apocalypse (as hybrids of polar bears and brown bears are
sometimes presented in the media). I also want to go into the role of hybrids
in conservation with reference to one particular case, the wisent Bisonbonasus.

The role of hybridization in speciation

Speciation
is the event of the evolution of a new species. Most species evolve either through
anagensis or cladogenesis. Anagenesis refers to the case of one species
directly evolving into another. Cladogenesis is the evolution of new species by
the split into new evolutionary lines, called clades, caused by reproductive
isolation. In both cases, the genotype gets transformed by mutation, selection
and genetic drift. But there is a third way a new genotype and a new species
can involve, hybridization. In this case a new genotype is formed by the mixing
of alleles respectively genes between species that are not too distantly
related so that they are not (fully) reproductively isolated yet. Usually
hybridization is constrained by pre- or postzygotic isolation mechanisms, and
even when two species produce fully fertile offspring the hybrids may have a
lower reproductive fitness than their parent species because they are less
suited to the ecological niches of their parent species respectively. But in
some cases, such as during the shift of environmental conditions or colonizing
a new environment, hybridization and the resulting new genotype can be
advantageous.

The plant
kingdom is rich with such examples, especially polyploid hybrids such as Tragopogonmiscellus. Both T. dubius
and pratensis have been brought to
North America by man, hybridized in nature and formed a stable hybrid via
polyploidization in the 1940s, T.
miscellus. In this case a novel species has been created. Other plant examples
are to be found in the “genera” Brassica
and Triticum.

There are
not only examples for plant species that evolved through hybridization or
introgression (introgression is when hybridization leads to an influx of genes
into one gene pool), but also plenty for mammals.

The “genus”
of modern Capra, goats, evolved
through hybridization between the ancestors of Capra and Hemitragus, a
closely related group, and as a result all modern Capra share Hemitragus
mtDNA1.

The
phylogenetic tree of Equus apparently
also experienced at least four events of hybridization or introgression (the
kiang and the donkey lineage, the Somali wild ass and the Grevy’s zebra, the
African asses and the mountain zebra)2.

The
Caribbean bat species Artibeusschwartzi is a stable, locally adapted
and morphologically distinct hybrid of three congeneric bat species3.

In
elephantid evolution, there must have been some interbreeding as was recently
revealed by ancient genomes. Palaeoloxodon antiquus interbred with both the woolly
mammoth Mammuthusprimigenius as much as with the Asian
elephant Elephasmaximus4.

Mutual
introgression and hybridization has been confirmed between the Alerigan mouse Musspretus
and three subspecies of the house mouse Musmusculus5.

Even in
marine mammals there is at least one confirmed case of speciation through
hybridiziation: the clymene dolphin Stenellaclymene is a hybrid species of the
spinner dolphin Stenellalongirostris and the striped dolphin Stenellacoeruleoalba6.

The phylogeny
of modern bears has experienced mutual hybridiziation as well, between the Asiatic
black bear and the ancestor of polar, brown and American black bear7.
Brown bears and polar bears repeatedly
admixed ever since they split up phylogenetically8.

All recent
Panthera species evolved under continuous intermixing between their
evolutionary lines9.

Moving to
species more relevant for the topics of this blog, bovines, we also have some
examples in this group. Cambodian banteng populations share mitochondrial
genetic material of the Kouprey, which they acquired probably through
introgressive hybridization during the Pleistocene10. It is also
well-supported by genetic evidence that the wisent is a hybrid of aurochs and
Pleistocene bison, to be precise the maternal lineage was founded by aurochs
and the paternal by bison11,12.

Last but
not least concerning mammals, we humans Homosapiens are a prime example for
hybridization and introgression as well. Human populations north to the Sahara
interbred with Neanderthals, and as a result about 1-4% of the genome of
non-African people is inherited from Homoneanderthalensis13. In
some Asian populations we also find 4-6% inherited from the Denisova people (a
yet undescribed species)14, and there is evidence of gene flow from
a third archaic population15. So the diverse modern human global
population is the result of intermixing with at least even three different
species.

Before
going too much into detail, there is also evidence from birds and other
vertebrate groups. As an example, Darwin finches are known to hybridize, which
influences each others’ evolution16. In 2017, a Science
paper announced the rapid speciation of a new Darwin’s finch lineage through
hybridization17.

Now I have
listed plenty of examples that show that hybridization and introgression played
a role in the evolution of many different species and species groups, even and
especially us humans, and there would probably be more if more were tested. The
role of hybridization in vertebrate speciation should be considered
well-supported by these recent studies.

Hybridization in nature

Natural
hybridization not only occurs when lineages diverge or environments shift, but
also happen in nature on daily basis in certain cases. I am going to go over
these examples now.

Precisely I
am talking about hybrid zones that exist when neighbouring closely related
species interbreed. Classic examples are fire-bellied toads (Bombina), where the species Bombinabombina and Bombinavariegata have a hybrid zone through
Europe where their habitat overlaps. The hybrids are fully fertile, but have
reduced evolutionary fitness. This limits the reproductive success of the
hybrids, otherwise there would be a continuum between species. A wild case of
natural hybridization in amphibians is Pelophylax.
Pelophylaxlessonae and P. ridibundus often overlap in range and
produce fertile hybrids. These hybrids, known as the edible frog, however,
passes on only one complete parental chromosome set and therefore never
produces stable hybrids but the backcrossed offspring “reverts” to the parental
species. Thus, edible frogs are classified as a kleptospecies, Pelophylax kl. esculentus.

In Canis, there is also frequent hybridization
in the wild between the species. Gray wolves hybridize with golden jackals (for
the reference, see the Species concept article), coyotes (the hybrid
populations have been described as a separate species, Canisrufus, which is now
called into question), and, as long as you regard them as a separate species,
Timber wolves. Another mammal hybrid zone is that between the polar bear and
brown bear, which has been addressed above already. Among megaherbivores,
African savannah elephants Loxodonta africana and forest elephants Loxodonta
cyclotis hybridize readily in overlap zones and form hybrid populations4.

Another
classic example of a hybrid zone is that between the carrion crow (Corvuscorone) and the hooded crow (Corvuscornix), which differ in plumage
colour but are otherwise very closely related. Both species are also often
listed as subspecies of one species or even only colour variants, but the
subspecies issue will be treated in a separate post.

There are
also plenty of examples from other animal groups and of course also plant
species that form hybrid zones.

A special
case that involves hybrid zones is that of a ring species. The ring species
concept refers to a group of neighbouring populations that might also be
recognized as distinct species (in which case it is more of a species ring
instead of ring species), along an ecologic or geographic gradient. Directly
neighbouring populations or species can interbreed, but not those at the respective
ends of the chain. Examples for a ring species or species ring are salamanders
of the genus Ensatina or the bird
species Phylloscopustrochiloides.

Hybridization in conservation

Hybridization
is also relevant for conservation. It is mostly considered a problem, even
called “genetic pollution”. Why is that, considering that hybridization
seemingly is a natural element of evolution and occurs frequently in the wild?
There are, one the one hand, good reasons for that which I am going to outline
now. But there are also examples and circumstances that should allow a
reconsideration of regarding hybridization/introgression as “genetic
pollution”.

When cases
of hybridization or introgression are referred to as genetic pollution it is
because it is of anthropogenic cause either through invasive species, domestic
animals or migration caused by climate change. A consistent influx of alien
genetic material alters the allele frequency and diminishes the autochthonous
genetic material, the genetic integrity, to a level that a species can go
extinct on a genetic basis. This is especially a danger in populations or
species that are already endangered. One example for a subspecies that has been
lost through hybridization is the Barbary lion, Panthera leo leo. It is extinct in the wild, and in captivity zoos
did not pay attention on not to mix subspecies. Nowadays, many lions in
captivity that are managed without subspecies classification descended from
Barbary lions, but there are no pure representatives of the clade anymore19.
There has been announcements for a project to genetically breed-back the pure
form, but the project seems to have died a silent death.

Mallard
ducks Anasplatyrhynchos have been introduced in various regions of the world,
and they threaten the genetic integrity of numerous autochthonous species, such
as A. rubripes, A. fulvigula, A. wyvilliana and A. superciliosa.
American ruddy ducks Oxyurajamaicanensis threaten European A. leucocephala20.

The
endangered Californian tiger salamander Ambystomacaliforniense is threatened by
hybridization with the introduced Barred tiger salamander A. tigrinum, and the
hybrids themselves cause ecological problems21. From the same
salamander group, the Axolotl, is very endangered as well, and in aquarist
keeping they sometimes are consciously crossed with tiger salamanders to
produce more colour variants. Due to the lack of a transparent breeding book,
this could become a problem for the species’ genetic integrity.

Moving back
to mammals, another well known example of “genetic pollution” is the American
bison. When the American bison went through the severe bottleneck at the end of
the 19th century, herd keepers experimented with cattle hybridization.
Nowadays, nearly all herds tested contain genetic traces of domestic cattle22.
The phenotypic legacy of this domestic cattle introgression can occasionally be
seen in modern bison, it mostly shows in deviant horn shapes or tails longer
than the norm for bison (see here, for example) although in most cases the
introgression is invisible. However, bison with cattle introgression may have a
fitness disadvantage under fully pure bison because they have a lower body mass
in the wild23.

Now we come
to the animal that concerns me the most, the European bison or wisent. In the
1920s, the species almost vanished due to hunting and habitat destruction, and
all modern wisent descend from only 12 individuals. During this massive
bottleneck event, there was intransparent hybridization with American bison and
also domestic cattle. It was feared that pure wisents are going to disappear,
which is why a breeding book was set up. Nowadays, the danger of pure wisents
becoming swamped out by hybrids has been banned. Most modern wisent have a
confirmed pedigree. They are pure but their extremely narrow gene pool is a
drastic danger for the existence of the species. Epidemics and developmental
problems cause high mortality rates or miscarriages both in the wild and zoos which
is seen as a danger for the long-term survival of the species24. The
hybridization with American bison back in the 1930s have mostly been executed
in order to increase the genetic diversity and therefore reduce the impact of
the severe inbreeding depression. While most of the hybrids have been culled
later on, there is a Wisent population in the Caucasus mountains that still
contains about 5% American introgression. It is phenotypically recognizable to some degree (see here). These “hybrids” are frowned upon some
conservationists for phenotypical and ecological reasons that I cast in doubt
in this post, and are the largest connected wild population of wisents with the
longest history. Although it has not been directly tested, I think there is
good reason to assume this population is healthier and has a higher
evolutionary fitness due to the increased genetic diversity that is also under
natural selective pressure. Therefore I actually consider this population very
valuable, while some conservationists propose its extermination as it might be
a danger for the purity (and thus genetic scarcity) of neighbouring wisent
populations. In my opinion, the health and fitness of the Caucasus population
should be evaluated, and if it indeed turns out to be higher or considerable
higher than in pure and thus highly inbred wisents, which I assume to be
likely, one might consider creating a third wisent breeding line with
controlled transparent hybridization that aims to conserve the genetic
integrity of the species but at the same time provide new allelic variation to
overcome its sensitivity to diseases and developmental problems. I proposed
this in the post linked above, and also donated for the wisent in the Caucasus.

Because it
is my fear that the drastically narrow genetic diversity of the wisent might
one day lead to animals that are pure on the one hand but not robust enough to
establish and maintain wild or even captive populations, and that the wisent
one day might not be able to survive on the long-term sight.

The main
problem is the academic acceptance. All the studies I have cited in this posts
are of recent years, therefore the numerous examples that underline the role of
hybridization and introgression in species are known only since a short period
of time. It will require some further studies and more years to pass until this
knowledge has found its way into mainstream science and consciousness, and once
it becomes accepted, it will start to influence conservational practise. Part
of the problem also is that the out-dated concept of the 19th and 20th
century of nature as a stable, balanced system that only changes in once in
considerable geological timespans and of species as static entities with a
clear, always tree-like phylogeny seems to be prevalent in the mind of many
conversationalists, although modern science establishes a concept of nature as
a dynamic system of constant changes that can also occur in a short period of
time.

Conservationists
have good reasons to condemn hybridization and introgression in most cases,
especially uncontrolled in the wild, but there are also cases, such as in the
wisent, where controlled and transparent hybridization or introgression could
actually be beneficial for the survival of the species.

Thursday, 8 February 2018

Before I
continue with my Biological basics series I want to announce an idea that I
have been thinking about for some weeks now. A couple of people told me that I gathered
so much material on the Breeding-back blog in the form of literature
references, information on projects, trips, reports, photos, artworks and own
theories that it would be worth to publish all that as a book. I like that idea
pretty much and I am confident that I can accumulate enough material to fill a
comprehensive book with it, so I have been working on a preliminary table of
contents for now.

What is
important is that this book would not be a mere copy+paste collection of
articles of the BBB, not at all. It will be a well-structured work that
collects all the material of the blog topic by topic, goes more in-depth and
will be precisely researched and referenced. Of course it will give a precise
overview over the history and present of the major breeding-back projects,
breeds involved and results. And it will also cover a couple of animals other than
horses, cattle and the quagga. I will extend articles with new data and more
profound research and I am also going to cover aspects that have not been
addressed much on the BBB before. I would also present new artworks and photos
that I am currently working on or have not published yet so far. Therefore,
even if you have been a rigorous reader of the blog from the first moment on,
you would find a lot of new material in it and also find it a clear and
structured reference work which is way handier than hundreds of loose single
articles published in the web.

The book
would probably be written and published as an ebook. This would make it easier
for me than looking for a print publisher, because the topic of the BBB is
rather special. Now, the question for my readership is: what do you think about
my idea, would you be interested in having a comprehensive, in-depth and
well-structured ebook version of the BBB that also contains a lot of new
information and picture material?

I am highly
motivated and looking forward to start with the work for the book. I will keep
you up to date and present information on title and the new material that will
be found in it during the next weeks or months.

Monday, 5 February 2018

Todays post
is on a rather theoretical topic, namely the definition of a species. It is
very basic, but a necessary requirement for other issues such as hybridization
or the subspecies concept, which are relevant for several units of
“breeding-back”. At first it might seem easy to define a species, but everybody
who has a basic deeper knowledge of biology will know that it is actually a
very tricky issue. There are several concepts and definitions of a species, and
none of them qualifies as the ideal and only one. This is why there is the
saying “in a room of n biologists there
are n+1 species definitions”.

The reason
for this problem is that the taxonomical system that classifies organism is an
artificial one made by us humans in order to work efficiently with the
diversity of living beings. Classical Linnean ranks, thought to us in school
and common to most people having a basic biological knowledge, are painfully
artificial and subjective which is why they are usually avoided in modern
phylogenetic systematics and cladistics. The basic biological entity that systematics
are based on are individuals (even here we have blurred lines, see animal
colonies; however, this blog deals only with vertebrates so let us ignore those
for now). The next level are populations, and above that, biological ranks begin
and so does subjectivity. Strictly spoken, a species is more of a hypothesis
than an entity. In this post, I want to outline the different approaches to how
define a species, their problems and also give some examples.

We want to
focus on vertebrates here. For other organismic groups, such as the asexually
reproducing bacteria, there are other approaches on how to define a species. The
most common species definition was coined by Ernst Mayr and is widely known as
the biological species concept. As “biologic” is rather generic, I refer to as
the Mayr’s definition in this post. It defines a group of individuals or
populations that actually or potentially reproduce and produce fully fertile
offspring. This concept works well in many cases, which is why it is widely
used. But there are also examples where it becomes problematic. One problem are
hybridization in the wild; many species have hybrid zones with closely related,
neighbouring species. Prominent examples are fire-bellied toads (Bombina), or Canis, where wolves hybridize with golden jackals in Eurasia1
and coyotes in North America, and so do the so-called pariah dogs2. A
special case of hybridization in the wild that makes the Mayer’s definition problematic
are the so-called ring species. Another example that is relevant for us are
American and European bison (Bisonbison and Bisonbonasus). Both are geographically
isolated because they dwell different continents, but when brought to the same
area they reproduce readily and produce fully fertile offspring. This is why some
authors have suggested listing them as one species, giving them subspecies
status (although both the European and American bison are further divided into
two subspecies themselves). However, most zoologists still consider both
different species. One reason is another level that is relevant for species
recognition, morphology. There is the so-called morphological concept or
morphospecies that differentiates species based on phenotypical traits. Palaeontologists
mostly have to work with morphospecies only due to a lack of genetic, ethologic
and ecologic data. The problem of morphospecies are intraspecific variation,
which can also lead to a morphologic overlap between closely related species,
as much as phenotypic plasticity. The ambiguity of the morphospecies concept
shows for example in the case of lion (Pantheraleo) and tiger (Pantheratigris). The
skeleton of a female tiger and a male lion are almost indistinguishable3.
However, apart from other morphological differences such as coat colour and
hair growth (mane), lions and tigers have different social behaviour, hunting behaviour
and despite an overlap in range do not reproduce in nature, which is why they
are considered separate species. This, as much as the bison example, shows that
in practice not just one species definition but often a mix of several levels
(genetic, morphologic, ethologic and ethologic) is used to determine and
differentiate species.

The third
relevant definition of a species is called the phylogenetic concept, which
deals with species that evolved through cladogenesis (that is the split of
evolutional lines; the direct evolution from one species to another without
cladogenesis is called anagenesis). In this case a species is a monophyletic
clade of one or more population that ends either through speciation (the
evolution of a new species) or extinction. This concept is only useful under
the frame of phylogenetic systematics or cladistics.

Having had
a look at what species actually are, we can dive deeper into the issues of
hybridization and subspecies, which is directly relevant for “breeding-back”
related topics concerning the wisent, quagga and others that have been covered
here on this blog.

About this blog

This blog is on everything related to the so-called “breeding-back” of extinct animals: From the extinct animals themselves, over their often domestic descendants and dedomestication to news and facts about various breeding-back projects, reports and photos from my own breeding-back related trips. I try to have a balanced and fact-based approach to this subject and to dismantle many of the popular myths. Enjoy!

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About me

My major interest always have been extinct animals, from dinosaurs to Pleistocene megafauna and more recent extinctions. Besides that I am interested in evolution, genetics and ecology.
I am also an amateur animal artist, making drawings and models mostly of extinct animals.